The invention relates to a linear drive comprising a housing, which defines a receptacle, in which drive means are arranged and out of which at least one axial end region of a power transmission member, which is adapted to cooperate with the drive means, extends.
Linear drives of this type are in wide use in the form of fluid power components, that is to say components operated by fluid. One possible design is to be found in the German patent publication (utility model) 29,706,098.8, which involves a linear drive designed in the form of a slide drive device and whose principal housing body comprises a cylindrical receptacle, wherein a piston constituting the drive means slides. A rod-like power or force transmitting member, connected with the piston, extends at its end out of the principal housing body and is able to be coupled with an object to be moved.
The actuation of the linear drive is performed by the action of a fluid on the piston and for positioning external abutments are provided.
In the case of linear drives of this type there is usually the problem that more especially in the case of pneumatic operation precise positioning of the power transmitting member is difficult and that slow movement of the piston tends to be jerky, this impairing exact motion and positioning.
One object of the present invention is to provide a linear drive of the type initially mentioned, which facilitates any necessary positioning measures and more especially renders possible jerk-free motion even at low speeds. This is to be combined with a simple structure of the arrangement, which is simple to assemble and fit.
In order to attain this object there is the provision in accordance with the characterizing part of claim 1 that the drive means are components of a linear electric motor, which is mounted in the receptacle as a cartridge-like unit and is fixed in relation to the housing.
Departing from the said prior art there is therefore an electrical linear drive, whose drive means belong to a so-called linear motorxe2x80x94a particular design of an electric motorxe2x80x94in the case of which the armature does not perform a rotary but rather a linear movement. The drive force is provided by a travelling magnetic field, this meaning that even in the case of slow motion there is a freedom from jerks and there is possibility of extremely smooth movement. Furthermore, such a linear motor is also characterized by low wear and reduced need for servicing.
It is furthermore an advantage in the invention that the linear motor does not have its individual parts fixed to the housing and is in fact inserted into it like a cartridge, the housing not having to perform any important operational function for the electrical drive principle of the linear motor. Accordingly it is possible for the housing to possess a configuration in accordance with the intended purpose of use, the external form not having to be different to that of a comparable fluid power linear drive and it is only instead of the drive means in the case of fluid power linear drive means the electrical linear motor may be employed. In this respect it is an advantage that in case of need, on the basis of a uniform housing, a fluid power or an electrical linear drive may be produced, that is to say with the possibility of employing a large number of identical parts. Finally, it is to be noted as an advantage that lost time due to a defect in the drive means and involving failure to operate of the linear drive may be very considerably reduced, because the cartridge-like linear motor unit may be simply and rapidly replaced.
Although the German patent publication 19,512,080 A1 discloses an electrical linear drive, in whose housing an electrical drive is inserted, recourse is had here to a conventional electric motor with a rotating drive shaft and furthermore there is no design in the form of a cartridge-like unit.
Further advantageous developments of the invention are defined in the dependent claims.
The linear motor preferably possesses a tubular or sleeve-like motor housing extending along at least part of its length, which extends into the receptacle in the housing, optimum fitting in place being ensured because the shape thereof is complementary to the internal shape of the receptacle space. In this respect it is preferred to employ a circular cross sectional shape owing to the possibility then offered of particularly simple manufacture. It would be feasible also however to have cross sectional forms departing from a circular one, more particularly if using simple means it is desired for the linear motor unit to be locked in rotation in relation to the housing.
Insertion of the linear motor into the receptacle may take place as part of a strictly linear plugging operation and/or for example by screwing in so that the assembly movement is combined with a rotary one. In this case it is possible for a suitable screw thread to be provided on the outer periphery of the motor housing to cooperate with a mating thread on the housing.
It is convenient for the receptacle, which preferably extends along at least the major part of the length of the linear motor, to be closed peripherally along its entire length, i. e. not interrupted by slot. It is possible to avoid having a special purpose design and there is the possibility of having recourse to the comparable body of a conventional fluid power linear drive for the housing.
The receptacle is preferably constituted by an elongated receptacle space extending in a principal housing body of the housing, into which space the linear motor unit is inserted like a cartridge coaxially from one end. In the case of the principal housing body it is preferably a question of extruded section, into which the receptacle space is produced in an axially continuous form.
It is preferred for the linear member to possess a motor housing arranged at least for the greater part of the length thereof in the interior of receptacle space, the power transmitting member extending from one end of it while adjacent to other end there are electrical terminal means for the supply and/or output of electrical signals, the electrical terminal means preferably being part of a compact coupling means.
Operation with a high degree of accuracy is possible, if the power transmitting member engages a guide slide, which slides externally on the housing linearly. Such a guide slide or carriage can also take up transverse forces so that the drive means, cooperating with the power transmitting member, of the linear motor can be kept substantially free of transverse loads causing wear.
Frequently electrical linear drives are in competition with fluid power linear motors, the use of one or the other type being specified by marginal conditions of the respective application. One serious disadvantage in connection with this is that the different types, as confirmed by the German patent publication (utility model) 29,706,098.8 and the German patent publication 19,512,080 A1, are extremely different so that the manufacturer do not supply both types in all overall sizes and the user is obliged to make extensive design changes in drive systems for adopting a different sort of drive. The electrical linear drive in accordance with the invention does offer the advantage here that for the production thereof recourse may be had to a single principal housing body, which may be employed alternatively as well as the principal housing body of a fluid power linear drive. For this purpose there is a provision such that the principal housing bodies in both types of linear drive are the same in their outer shape at least and the receptacle spaces provided in the principal housing bodies of the linear drive possess the same cross sectional form. Accordingly for the manufacture of the principal housing bodies one may resort to substantially identical steps and tools, this meaning that there is also compatibility for the user. The identical cross sectional form of the receptacle spaces leads to a flexible manufacture, since, dependent on the type of design, it is merely necessary for fluid power or electrically operated drive means to be inserted.